The present invention relates to compositions and methods for controlling plant pathogens by contacting the plant or the soil which surround the plant with a composition comprising an effective amount of at least one metal ion, at least one chelating agent and at least one phosphorous acid, a salt or hydrate thereof.
Global regulatory requirements are becoming more and more demanding with respect to the use of pesticides, particularly with respect to unmanaged or unnecessary pesticide residues. Thus, there exist mutually contradictory requirements of farmers in that the need to control destructive pathogens demands that more pesticide be used, while increasing pressures from regulatory agencies demand that less pesticide be used. These regulatory demands are aimed to protect the safety and health of agricultural workers and the general public. It is also well-known that the general public would like less chemical residue on fruits and vegetables. A particular consequence of this situation is that there is an increasing need to have more efficient methods of protection of plants such as fruits and vegetables.
The control of phytopathogenic fungi is of great economic importance since fungal growth on plants or on parts of plants inhibits production of foliage, fruit or seed, and the overall quality of a cultivated crop. Because of the vast economic ramifications of fungal propagation in agricultural and horticultural cultivations, a broad spectrum of fungicidal and fungistatic products have been developed for general and specific applications.
Inorganic substances were the first to be used in large-scale crop protection aimed against pathogenic fungi. Notable among these are elemental sulfur applied in powder form, and copper sulfate applied in caustic calcium aqueous mixture (Bordeaux mixture). More complex, synthetic, organic compounds and combinations of organic compounds with metals were developed over the past century with concomitant rise in specific efficacy per unit weight of the active matter. However, such compounds are often environmentally non-recyclable or some of their derivatives are found even toxic to wild life in the environment. Additionally, pathogens often develop resistance to such synthetic pesticides, a fact that promotes a continuous endeavor for developing new crop protecting agents.
In spite of the development of organic chemistry of pesticides, the use of simple structured anti pathogenic compounds has not declined, and constantly new ideas and products of this trend are being unveiled. Fungicide compositions based on copper, zinc or manganese are known to be effective against a broad range of plant pathogenic fungi and bacteria. These include copper hydroxide (Kocide), copper sulfates (Bordeaux mixture), copper oxychlorides and copper oxide. The estimated use of copper hydroxide in the U.S.A. in 1995, for example, was approximately 5 million kg. The reasons for using simple inorganic compounds for control of plant disease are twofold: first, most of the pesticides in this category are environmentally recyclable, and second, the pests do not tend to develop immunity against them. These compounds act upon contact and are applied mainly by foliar spray. The use of these traditional inorganic fungicides for soil treatment is limited due to the absorption of the metal ions to soil particles.
Chelating agents have been used in agriculture for decades as fertilizers of microelements essential for plant growth, i.e. iron, zinc, manganese, copper, etc. The chelating molecule improves the mobility of microelements in the soil, thus enabling the delivery of microelements to the root zone. In addition, the chelating molecule protects the availability of microelements for intake by plant roots.
The combination of metal ions and chelating agents (chelated metals) may be used as effective fungicides for plant disease control as claimed in the Israeli patent IL 97676. However, chelated metals fungicides are phytotoxic at optimal fungicdal dose and therefore not commercially practical.
Phosphorous acid (H3PO3) or phosphorous acid salts (phosphites or phosphonates) are known to be active against Oomycetes fungi. The mode of action of phosphite as an antifungal agent, involves both direct fungal inhibition as well as induced resistance. The use of compositions containing phosphites for plant disease control was disclosed in U.S. Pat. No. 5,674,536. Said patent discloses fungicide compositions whereby the active substances are a phosphite salt, lecithin, and at least one of the two compounds selected from sodium metasilicate and soda waterglass. U.S Pat. No. 4,075,324 discloses the use of phosphorous acid or the salts thereof as effective fungicides for controlling fungus disease in plants.
The disadvantages of the above described phosphite salt-based compositions and methods relate to their limited efficiency in reducing disease severity relative to alternative synthetic organic fungicides. Moreover, the above described compositions are in a form of a spray and can not be applied directly to the soil since phosphite salt-based compounds tend to be absorbed by soil particles, thereby decreasing their uptake by plant roots.
Thus, it will be highly advantageous to have a safe, environmental recycable and user friendly composition and a method for controlling plant pathogens, that will be efficient and cost effective and will treat and protect plants against foliage and soil-borne pathogens.
The invention provides a composition for controlling growth of pathological organisms on a plant, said composition comprises an effective amount of one or more of metal ion(s); one or more of chelating agent(s); and phosphorous acid, and/or salt or hydrate thereof, said composition is in an agriculturally compatible carrier or vehicle.
In preferred embodiment, the composition further comprises an acidifying agent so as to form a low pH solution, Lower pH increases the solubility and uptake of metal ion into the roots of plants.
The chelating agents provide a protective coating over metal ions and prevent the absorption of metal ions in soil particles, and increase both the metal""s solubility in water and its mobility in wet soil.
The invention further provides a method for controlling growth of pathological organisms on a plant, said method comprising contacting said plant or the soil which surround the plant with an effective amount of a composition comprises one or more of metal ion(s); one or more of chelating agent(s); a phosphorous acid and/or a salt or hydrate thereof, said composition is in an agriculturally compatible carrier, whereby growth of said pathological organisms on said plant is controlled.
The components of the composition possess unexpectedly synergistic interaction of controlling growth of pathological organisms on a plant. Thus, the surprising synergistic activity of the components of the composition of the invention provides an environmentally recyclable solution, which is applicable as both a protective and a curative disease control treatment. The presence of the three different components in the composition that possess synergistic activity prevents the development of resistance by pathogens, provides additional nutritive plant-growth benefits, decreases the cytotoxicity of fungicides to human and mammals and enables a user-friendly method of administrationxe2x80x94applicable via the irrigation system.